The present invention is directed to an improved apparatus for detecting wheel spin-up in a brake control system.
Vehicles such as modern jet transports are provided with sophisticated braking systems, which commonly include anti-skid control systems as well as automatic braking systems. U.S. Pat. No. 4,022,513, which issued May 10, 1977 to Edgar A. Hirzel and Robert D. Cook and is assigned to the assignee of the present invention, discloses one such brake control system. This system operates automatically to apply brake pressure to initiate braking action during landing immediately following aircraft touchdown. This patent is hereby incorporated by reference for its discussion of the general background of one such automatic braking system.
An important consideration in automatic braking systems is that the brakes should not be applied until after the wheels have approximately reached synchronous speeds. If the brakes are prematurely applied before the wheels have spun-up to nearly synchronous speed, tires can be severely damaged by the resulting skids. In the past, one approach to this problem has been to provide a velocity threshold, such that the brakes are not applied until after the wheel has spun-up beyond a predetermined velocity.
The use of a velocity threshold to indicate that wheel spun-up is substantially complete brings with it certain disadvantages. First, a fixed threshold velocity cannot take into account differences due to variations in landing speeds. It is common for landing speeds to vary within a range of twenty knots or more during routine service. A single fixed threshold velocity appropriate for landings in the lower range of landing velocities will prematurely indicate that wheel spin-up is substantially complete during a fast landing. This will result in the automatic braking system prematurely applying brakes before the wheel has accelerated to substantially synchronous velocity, which may in turn result in excessive wheel skids.